This study evaluates the physiologic effects of levodopa (an oral dopamine analogue) on cardiac function in children with congestive cardiomyopathies and examines the pharmacokinetics of the drug in relation to the observed hemodynamic effects over a 1-month study period. Dose escalation of the medication and concomitant acquisition of serum catecholamine levels are performed over an initial 3-day period. More precise hemodynamic effects are then determined by cardiac catheterization.